Regenerative air preheater with stationary cylindrical regenerative chamber

ABSTRACT

A regenerative air preheater with a stationary cylindrical regenerative chamber following a steam generator, in which the flue gases flow through the stationary regenerative chamber via hoods which rotate coaxially with regard to each other at their end faces. One of said hoods is surrounded by the air withdrawing passage whereas the other one of said hoods is surrounded by the air in-feeding passage, the diameter of the central circular neck cross section of the rotary hood at the flue gas discharge side amounting to from 0.35 to 0.5 times the diameter of the regenerative chamber whereas the axial height of said rotary hood amounts to from 0.2 to 0.3 times the diameter of the regenerative chamber.

[451 Apr. 9, 1974 REGENERATIVE AIR PREI-IEATER WITH STATIONARY CYLINDRICAL REGENERATIVE CHAMBER lnventors: Franz-J. Kirchhoff; Erich Kraft,

both of Huttseifen, Germany Assignee: Apparatebau Rothermuhle Brandt & Kristzler, Wenden, Germany Filed: May 18, 1972 Appl. No.: 254,420

Foreign Application Priority Data May 18, 1971 Germany 2124584 U.S. Cl 165/4, 110/56, 165/7 Int. Cl..... F28d 17/04 Field of Search 165/4, 7; 110/56 References Cited UNITED STATES PATENTS 5/1965 Johnstone 165/4 3,233,661 2/1966 Firgau et al 165/4 X Primary Examiner-Albert W. Davis, Jr. Attorney, Agent, or Firm-Walter Becker ABSTRACT A regenerative air preheater with a stationary cylindrical regenerative chamber following a steam generator, in which the flue gases flow through the stationary regenerative chamber via hoods which rotate coaxially with regard to each other at their end faces. One of said hoods is surrounded by the air withdrawing passage whereas the other 'one of said hoods is surrounded by the air in-feeding passage, the diameter of the central circular neck cross section of the rotary hood at the flue gas discharge side amounting to from 0.35 to 0.5 times the diameter of the regenerative chamber whereas the axial height of said rotary hood amounts to from 0.2 to 0.3 times the diameter of the regenerative chamber.

3 Claims, 2 Drawing Figures The present invention relates to a regenerative air preheater with stationary cylindrical regenerative chamber which follow a steam generator and in which the flue gases in a manner known per se flow through the stationary regenerative chamber via rotatable hoods which at their end faces rotate coaxially and synchronously. One of the hoods is on all sides surrounded by the air feeding passage whereas the other one of the hoods is on all sides surrounded by the air discharging passage.

It is an object of the present invention to provide a particularly favorable design and arrangement of the feeding and discharging passages for the heat exchanging media, which feeding and discharging passages are connected to the stationary regenerative chamber.

With heretofore customary arrangements of the regenerative air preheaters having a stationary regenerative chamber following a steam generator, the air to be heated was passed through central air hoods which on both sides at the end faces of the cylindrical regenerative chamber rotate in stationary flue gas connecting passages. v

With such a design relatively low medium wall temperatures for the corrosion-endangered cold air hood were obtained, in particular in the flow ranges of the maximum retardation of the flue gases leaving the regenerative chamber which flue gases have been cooled down approximately to a temperature of 160C.

The velocity of this flue gas flow amounts at the exit cross section of the regenerative chamber approximately to 8 m/sec, and over the relatively short flow path in the vicinity of the neck cross section of the cold end rotatable hood it is slowed downto approximately 2.5 m/sec.

The velocity of the cold air flow which is substantially directed in opposite direction in this rotatable hood is on the average twice as high. At the neck cross section of the cold end hood the velocity amounts to approximately 15 m/sec and is slowed down to about m/sec up to the regenerator end face.

This relatively higher velocity of the cold air together with the tendency of the slowed down flue gas flow to detach itself from the outer walls of the rotatable hood, which tendency is caused by the shape of the widening of the cross section, brings about that the heat transfer coefficient between flue gas and wall is considerably lower than that between wall and air. As a result thereof, the medium wall temperature of the air hood lies considerably below the arithmetical medium value between flue gas temperature and air temperature and thus frequently also below the flue gas dew point or condensation point.

Therefore, in order to avoid corrosion due to dropping below'the dew point of the flue gases, it is necessary to produce the rotatable hood either of high grade corrosion-resistant and expensive steel or to design the rotatable hoods with a double wall and to protect the same by additional heat protective covers against such excessive undercooling. I

The invention is furthermore based on the finding that when providing the regenerative air preheaters with a stationary regenerative chamber and rotating air hoods within the stationary flue gas connecting passages, the arrangement of the air connecting passages so as to extend into the flue gas passages may from a structural standpoint be unfavorable and may interfere with the uniform distribution of the flue gases within the heating surfaces. As a result thereof, unilateral soiling of the heating surfaces and pulsation of the combustion air may result.

It is, therefore another object of this invention so to accelerate the flue gases that advantageous flow conditions and higher medium wall temperatures of the cold end hood will be obtained.

It is a further object of the present invention to-provide a regenerative air preheater as set forth in the preceding paragraph in which the flow passages for the heat exchanging media are structurally considerably more favorable.

These and other objects and advantages of the invention will appear more clearly from the following specification in connection with the accompanying drawings, in which:

FIG. 1 shows a prior art regenerative air preheater with stationary regenerative chamber.

FIG. 2 diagrammatically illustrates a regenerative air preheater according to the present invention as connected to a steam generator with vertical exit of the flue gases.

The regenerative air preheater according to the present invention is characterized primarily in that the flue gases pass through the stationary regenerative chamber through rotatable hoods which at their end faces rotate coaxially and synchronously, one of these hoods being surrounded on all sides by the air feeding passage while the other one of these hoods is surrounded on all sides by the air withdrawing passage, the arrangement being such that the diameter of the central cylindrical neck cross section of the rotatable hood at the flue gas discharge side amounts to 0.35 to 0.5 times the diameter of the regenerative chamber whereas its axial height amounts to from 0.2 to 0.3 times the diameter of the regenerative chamber.

According to a further development of the invention, the axial height of the stationary flue gas passages adjacent the central neck cross sections of the rotatable hoods is less than 0.4'times the diameter of the regenerative chamber. In certain circumstances, with the design of the regenerative air preheater according to the invention, the flue gas passage on the gas on-flow side may be completely omitted. The gas inlet hood may merely by the interposition of an expansion diaphragm be directly connected to the exit cross section of the last boiler flue path.

Referring now to the drawings in detail, it will be seen from FIG. 1 that the flue gases leaving the steam generator flow within the flue gas passage height h, around the stationary air discharge passage 5 which laterally extends out of the flue gas passage. The deviation of this passage 5 into horizontal direction requires a minimum height h for the installation and connection to the central neck cross section of the lower warm air rotatable hood 1 which amounts to approximately 0.4 times the diameter D of the stationary cylindrical regenerative chamber.

Similarly, the stationary air feeding passage 6 which follows the upper neck cross section of the cold air hood 2 is horizontally in the direction perpendicular to the drawing plane of FIG. 1 introduced into the flue gas exit passage and within the height 0.4 D is in axial direction deviated downwardly. The axial overall height of this passage arrangement between the upper edge of the air feeding passage 6 and the lower edge of the air discharge passage is designated with the character H,,.

At the cold end, on the gas discharge side, the cooled off flue gases flow when leaving the regenerator end face at a velocity of approximately 8 m/sec in the direction of the arrow 8 and slow down in the vicinity of the neck cross section of the cold air rotatable hood, where the arrow 9 is shown, to approximately 2.5 m/sec.

In contrast thereto, the air which within the cold air hood flows downwardly has in the neck cross section the medium inlet velocity of approximately m/sec as indicated by the magnitude of the arrow 10. This velocity slows down on its way toward the upper end face of the regenerative chamber to approximately 5 m/sec as it is indicated by the relative magnitude of the arrow 11.

The reversal according to the present invention and the structurally more favorable design of the channel means for conveying the heat exchanging media as well as the acceleration of the gas flow obtained thereby within the region of the cold end rotatable hood are illustrated in FIG. 2.

The cooled off flue gases pass in the direction of the arrow 12 approximately at a velocity of 8 m/sec from the end face of the regenerative chamber 12a and are accelerated in the cold end hood 2 up to a velocity of m/s in the direction of the arrow 13 within the neck cross section of this hood.

The warm flue gasses having a medium temperature of approximately 160C flow, in contrast to the flow conditions of heretofore known customary designs, at a considerably higher medium velocity and at accelerated flow along the walls of the cold end hood. The new arrangement according to the present invention thus makes it possible by correspondingly dimensioning the neck cross section diameter D, of the cold end hood greatly to increase the heat transfer coefficient between flue gas and wall and thereby the medium wall temperature in the corrosion endangered region so that, as a rule, no drop below the dew point will occur.

The arrows 14 in FIG. 2 and 15 in FIG. 1 indicate the downwardly directed air velocities in the air feeding passage outside the cold end hood which air velocities increase from approximately 3 m/sec to approximately 6 m/sec at the entrance into the regenerator end face. The reference numeral 3 indicates an expansion diaphragm.

Structural simplifications result, above all, with this arrangement from the lower height h and h of the central flue gas connecting passages l' and 2 of which, as the case may be, the flue gas inlet passage 1 may be completely omitted. As a result thereof, the flue gas contacted surface of the air passage is over the heretofore known design considerably reduced, and the damage due to and the necessary repair caused by possible corrosion will be correspondingly reduced. The lower structural height of the arrangement makes it possible to lower the center of gravity of the system in which the air preheater according to the invention is installed. This advantage is of particular importange with boiler installations in ships.

The present invention makes it possible with shorter smokestacks, and in particular with boilers in ships, to

accelerate the velocity of the flowing off flue gases to such an extent that also under unfavorable conditions of operation and servicing the soot and ash particles carried along by the gases will be definitely discharged from the smokestack. The immediate acceleration of the flue gases when leaving the regenerative chamber also brings about an increased self-cleaning of the heating surfaces.

The most important advantage inherent to the present invention consists in the increase of the medium wall temperature of the cold end hood whereby a drop below the dew point will be avoided and the corrosion resistant expensive steel materials heretofore employed for the manufacture of cold end hoods as well as the heat protective covers will no longer be needed.

It is, of course, to be understood that the present invention is, by no means, limited to the particular showing in the drawings but also comprises any modifications within the scope of the appended claims.

Thus, if desired, the pipe means 1 may be omitted and the neck portion of the hood means 2a may be connected directly to the adjacent pass or flue of the steam generator 16 with the expansion diaphragm 3 interposed therebetween.

ln summary, the following dimensional relationships of structure can be noted. A regenerative air preheater with a stationary cylindrical regenerative chamber follows a steam generator 16; the regenerative air preheater includes the stationary cylindrical regenerative chamber 12a, first rotatable hood means 1 arranged at one end face of the regenerative chamber for communication with the steam generator 16 and for receiving flue gases therefrom and conveying the same into the regenerative chamber; also included are the second rotatable hood means 2 rotatably arranged at the other end face of the regenerative chamber in coaxial arrangement with the first hood means 1 and adapted to receive flue gases from the regenerative chamber 12a. There are air discharge conduit means surrounding one of the hood means (1), air feed-in conduit means surrounding the other one of the hood means (2). The second hood means 2 decreases in diameter in the direction away from the regenerative chamber 12a and has a neck portion defining the discharge opening of the second hood means 2. There are flue gas discharge conduit means communicating with the neck portion; the diameter of the neck portion amounts to from 0.35 to 0.5 times the diameter of the regenerative chamber 12a; the axial height of the second hood means to from .02 to 0.3 times the diameter of the regenerative chamber 12a. In practice, the cross-sectional portion that becomes connected with the gas hood is one-half of the regenerator face surface or more. 1

What we claim is:

1. A regenerative air preheater, which includes in combination: a stationary cylindrical regenerative chamber, first rotatable hood means arranged at one end face of said regenerative chamber for communication with a steam generator with a vertical exhaust of smoke gases postconnected therewith and for receiving flue gases therefrom and conveying the same into said regenerative chamber, second rotatable hood means rotatably arranged at the other end face of said regenerative chamber in coaxial arrangement with said first hood means and adapted to receive flue gases from said regenerative chamber, air discharge conduit means surrounding one of said hood means, air feed-in conduit means surrounding the other one of said hood means, said second hood means decreasing in diameter in the direction away from said regenerative chamber and having a neck portion defining the discharge opening of said second hood means, and flue gas discharge conduit means communicating with said neck portion, the diameter of said neck portion amounting to from 0.35 to 0.5 times the diameter of said regenerative chamber, and the axial height of said second hood means amounting to from 0.2 to 0.3 times the diameter of said regenerative chamber, said first and second hood means being synchronously rotatable, said cylindrical regenerative chamber having an axis located in an extension of the middle vertical of the last flue gas conduit means.

2. A regenerative air preheater in combination according to claim I, in which said first hood means decreases in diameter in a direction away from said regenerative chamber and has a neck portion defining the flue gas inlet of said first hood means, first pipe means connected to said neck portion of said first hood means for connection to a steam generator and second pipe means connected to and interposed between said neck portion of said second hood means and said flue gas discharge conduit means, the height of said first and second pipe means being less than 0.4 times the diameter of said regenerative chamber to permit acceleration in velocity of flowing off flue gases and to bring about an increased self-cleaning due to less height.

3. A regenerative preheater in combination to claim 1, which includes an expansion diaphragm engaging the neck portion of said first hood means and adapted to engage the adjacent flue outlet of a steam generator to permit direct connection of said flue outlet to said second neck portion with only said expansion diaphragm interposed therebetween. 

1. A regenerative air preheater, which includes in combination: a stationary cylindrical regenerative chamber, first rotatable hood means arranged at one end face of said regenerative chamber for communication with a steam generator with a vertical exhaust of smoke gases postconnected therewith and for receiving flue gases therefrom and conveying the same into said regenerative chamber, second rotatable hood means rotatably arranged at the other end face of said regenerative chamber in coaxial arrangement with said first hood means and adapted to receive flue gases from said regenerative chamber, air discharge conduit means surrounding one of said hood means, air feed-in conduit means surrounding the other one of said hood means, said second hood means decreasing in diameter in the direction away from said regenerative chamber and having a neck portion defining the discharge opening of said second hood means, and flue gas discharge conduit means communicating with said neck portion, the diameter of said neck portion amounting to from 0.35 to 0.5 times the diameter of said regenerative chamber, and the axial height of said second hood means amounting to from 0.2 to 0.3 times the diameter of said regenerative chamber, said first and second hood means being synchronously rotatable, said cylindrical regenerative chamber having an axis located in an extension of the middle vertical of the last flue gas conduit means.
 2. A regenerative air preheater in combination according to claim 1, in which said first hood means decreases in diameter in a direction away from said regenerative chamber and has a neck portion defining the flue gas inlet of said first hood means, first pipe means connected to said neck portion of said first hood means for connection to a steam generator and second pipe means connected to and interposed between said neck portion of said second hood means and said flue gas discharge conduit means, the height of said first and second pipe means being less than 0.4 times the diameter of said regenerative chamber to permit acceleration in velocity of flowing off flue gases and to bring about an increased self-cleaning due to less height.
 3. A regenerative preheater in combination according to claim 1, which includes an expansion diaphragm engaging the neck portion of said first hood means and adapted to engage the adjacent flue outlet of a steam generator to permit direct connection of said flue outlet to said second neck portion with only said expansion diaphragm interposed therebetween. 